NAD+ precursor trials
Three names often travel together. The interesting work begins when the substance given and the substance measured get separate names.
Cellular NAD+
NAD+ has an established job. It helps cells move electrons through the reactions that turn food into usable energy, and it is consumed by enzymes involved in DNA repair, inflammation and gene regulation. The review of NAD+ metabolism during ageing describes several enzymes drawing on a shared supply.
There is something appealingly ordinary about this chemistry. The jump from essential chemistry to an anti-ageing treatment is where I become sceptical. Tissue NAD+ tends to decline with age, but the 2025 review of human supplementation found that consistent age-related decline had been documented in only a limited number of human studies. Information about individual tissues was sparse.
NAD+ itself enters cells poorly when taken intact. NR, nicotinamide riboside, and NMN, nicotinamide mononucleotide, are precursors: materials cells can use to make NAD+. They account for much of the controlled human work. A trial of one precursor answers a question about that precursor and its tested setting.
Blood measurements and muscle findings
The eight-week NR trial in healthy overweight adults reported blood NAD+ increases of 22%, 51% and 142% across its tested groups. Flushing did not increase and adverse events did not differ significantly from placebo. This is a persuasive demonstration that an oral precursor can change the blood measurement over the study period.
The sixty-day NMN trial in healthy middle-aged adults also found higher blood NAD+, alongside better walking distance and quality-of-life scores than placebo. Those functional results deserve to be remembered; reducing the whole literature to a blood test would flatten the interesting part.
In postmenopausal women with prediabetes, ten weeks of NMN improved muscle insulin sensitivity, meaning the muscle responded more readily to insulin. Body composition and the longer-term blood-sugar measure HbA1c did not change. I prize that precision: a response located in a tissue, with the other measurements still visible.
Across the collection, the open question is how these narrower changes translate into durable health. The human ageing review describes limited efficacy. None of these findings establishes longer life or broad disease prevention.
Infusions and long-term safety
An NAD+ infusion is a different preparation and route from an NR or NMN capsule. Controlled evidence for intravenous NAD+ is particularly limited; infused NAD+ is cleared rapidly from plasma. Infusions run too quickly can cause chest or abdominal discomfort, flushing and nausea. I would resist transferring the capsule trials' results to that setting.
There is also a manufacturing concern. The FDA issued its most serious kind of recall for a compounded NAD+ injection after elevated bacterial endotoxin was found. That was a contamination problem. Supplement purity and actual content can vary too, and external testing is not assured.
Cancer raises a separate, theoretical question. NAD+ supports cellular repair and metabolism, including processes that existing cancer cells can use. The effect can depend on the cancer. Short supplementation trials cannot settle long-term risk across those settings.
The FDA has disputed NMN's eligibility as a dietary supplement because it was investigated as a drug first. NAD+ has no approval as a drug; injectable preparations are typically compounded and are not FDA-approved. NAD+, NMN, NR and nicotinamide are not prohibited by the World Anti-Doping Agency. The legal labels and the biochemical findings describe different aspects of the same collection.